Polyolefin-coated photographic carrier material

ABSTRACT

A polyolefin-coated photographic paper coated with a crystallized coating of calcium, magnesium, zinc or lead fluoride or mixtures thereof, silicic acid and a matting agent is disclosed. The crystallized coating is receptive to hydrophilic substances and diminishes the hydrophobic nature of the polyolefin coating.

United States Patent S'averin et al.

[4 1 Oct. 21, 1975 POLYOLEFlN-COATED PHOTOGRAPHIC CARRIER MATERIAL Inventors: Eckehard S'averin; Jorg Zimmermann, both of Osnabruck, Germany Assignee: Felix Schoeller, Jr., Germany Filed: Feb. 20, 1974 Appl. No.: 444,045

Foreign Application Priority Data Feb. 22, 1973 Germany 2308711 US. Cl. 428/513; 96/85; 427/372;

427/411; 427/419; 428/538 Int. Cl. G03C l/87 Field of Search 96/85, 87 R, 87 A;

[56] References Cited UNITED STATES PATENTS 3,161,519 12/1964 Alsup 117/76 P X 3,525,621 8/1970 Miller 96/85 3,531,314 9/1970 Kerr et al. 117/76 P X Primary ExaminerRalph Husack Attorney, Agent, or FirmMolinare, Allegretti, Newitt & Witcoff 20 Claims, No Drawings POLYOLEFIN-COATED PHOTOGRAPHIC CARRIER MATERIAL BACKGROUND OF THE INVENTION protected by the polyolefin coating from the penetration of photographic treatment solutions. For example, when developing latent photographic images the raw paper is protected from the photographic treatment solutions.

Accordingly, closed films of polyethylene or polypropylene have been found particularly effective as a protective coating for the paper base.

A disadvantage of these polyolefin-coated carriers, however, is the fact that the conventional polyolefin coating material has a hydrophobic character. As a result coating materials and other solutions or emulsions of a hydrophilic kind which may be applied to these bydrophobic surfaces do not adhere. Thus, it is not possible to apply water-soluble adhesives directly to the hydrophobic surface of the polyolefin coating, or to make inscriptions on the hydrophobic surface by means of ball point pens, ink, felt pens, pencils and printing inks. The application of hydrophilic, light-sensitive photographic emulsions is also not possible without special treatment of the polyolefin coating surface.

A further disadvantage of this polyolefin coating is that it behaves as a dielectric. As a result, there is a tendency for the coating to become electrostatically charged. Such electrostatic charges frequently result in defects or other trouble during the further processing of the raw papers or during development of the emulsioned photographic carriers.

A further disadvantage of conventional polyolefincoated paper is the very smooth surface imparted by the polyolefins, i.e., a self-lubricating effect. For example, the smooth surface frequently disturbs the mechanical advance and transport of the photographic recording material in processing and developing machines, particularly, if the photographic carrier material is also coated at its rear side with a polyolefin layer, which in fact is indispensable for complete sealing of the surface of the paper against the penetration of water or photographic chemicals in solution.

To make the hydrophobic surface of smooth polyolefin coatings inscribable by means of hydrophilic colors, solutions or suspensions, it is known to activate the polyolefin surface by suitable activation methods. For example, the surface can be activated by a corona discharge with the use of high-voltage alternating current, by high frequency current or by the use of direct current with a superimposed alternating current. A photographic carrier material provided with the polyolefin layer or layers is guided through a gap which is formed at one side by a grounded guide roller for the strip-form material, whereas on the other side an electrode extends over the strip and is connected to high voltage.

An activated polyolefin surface can also be prepared by applying a water-solublefilm-forming agent to the surface. For example, a film-forming agent having a base of cellulose derivatives or polyvinyl alcohol is applied by itself or in conjunction with colloidal silica dispersed therein to the smooth suface. This layer or coating can then be written upon with aqueous inks or colors after drying.

It is also known to incorporate anti-static agents in the polyolefins or to apply anti-static agents in the form of a thin coating to the polyolefin surface, to eliminate the electrostatic charging of the polyolefin-coated carrier material. This coating containing anti-static agent is frequently a hydrophilic coating. The adhesion of the hydrophilic coating to the hydrophobic layer is carrier out, as already mentioned, by the activation of the hydrophobic coating, for example by corona discharge.

It is also known that the polyolefin surface can be activated to provide adhesion properties for hydrophilic coatings by applying an acid, aqueous mixture of an aqueous silica sol, an acid resistant organic filmforming material and an acid with a pH value between 2 and 7, to the surface and then drying the resultant coating at an elevated temperature or room temperature. After drying, this film is heated to elevated temperatures and the resultant film has absorbing properties.

Finally, it is known that the activity of the per se inactive surface of the polyolefin coating material for hydrophilic substances, brought about by corona discharge, decreases in the course of time, and renewed activation must be carried out if a relatively long time interval has elapsed between the activation and the subsequent coating of the carrier material for example with photographic emulsion. The time in which the activation dwindles depends on various factors, for example the relative air moisture and other environment influences. The activated surface can, of course, be conserved or put to its intended use directly if an adhesive coating of a hydrophilic character is applied to the activated surface and further coatings for example photographic emulsions, are then applied to the hydrophilic coating.

All of these additionally applied coatings which are intended to bring about the promotion of adhesion between hydrophilic substances and a surface which is hydrophobic in itself, however, have a considerable disadvantage since all of them include a film-forming agent, for example a polyethylene emulsion or a cellulose derivative and an agent or pigment which is dispersed therein and which has the actual hydrophilic properties, for example, the silica sol. Thus there is formed a coating in which the silica particles are distributed in the film-forming agent and are connected both to the surface of the polyolefin and to one another. Each particle, however, is substantially without any secure bond with the adjoining particle. As a result, the mechanical cohesion is of course slight, and the embedding of the silica particles in the film-forming material makes this coating relatively thick, and the thickness is substantially invariable.

SUMMARY OF THE INVENTION The present invention thus has as its object to provide a coating for surfaces of polyolefin layers on photographic carriers which will make the polyolefin surface or surfaces suitable both for coating with hydrophilic substances, solutions or dispersions and also for the application of anti-static agents, so that with a single coating of this kind all of the aforesaid disadvantages of polyolefin surfaces are eliminated, and the selflubricating effect of the polyolefin coating, more particularly in the case of a rear-side coating, is eliminated.

According to the present invention this is achieved in that on the polyolefin surface of the photographic carrier material, preferably activated by the known corona discharge method, there is deposited a crystallized coating consisting of a calcium, magnesium, zinc or lead fluoride or mixtures thereof, silicic acid (Si (H),) and a matting agent.

This coating for the surface of the polyolefin coating of a photographic carrier material is a layer intergrown by crystallization which is united, in this crystallized form, with the activated polyolefin surface. Due to the crystalline intergrowth between the polyolefin and the coating, the coating has excellent mechanical strength, which is particularly important when inscribing or printing on the coating. The crystal structure or the crystal crop can be arranged by variation of crystallization conditions, before and after application, so that an optimum condition can be obtained for different intended uses.

DETAILED DESCRIPTION OF THE INVENTION This crystalline coating is produced by applying to the surface of the polyolefin layer of a photographic carrier an aqueous solution or suspension containing a self-bonding silica sol, a salt of hexafluoro silicic acid, for example a calcium or magnesium salt of hexafluoro silicic acid and a matting agent, preferably, having a base of calcium silicate or calcium carbonate. If desired, this dispersion may also contain an anti-static agent, that is to say a conductivity agent for eliminating electrostatic charges, and possibly other additives.

Between the three constituents of this solution or suspension, namely the silicic acid sol, the salt of hexafluoro silicic acid and the matting agent having a base of basic calcium silicate or basic calcium carbonate, a chemical reaction and crystallization occur. In this reaction, the hexafluoro silicate reacts with the alkaline calcium compounds at the surface of the pigment particles with formation of calcium fluoride and silicic acid, both of which are very difficultly soluble.

Instead of the calcium salt of hexafluoro silicic acid it is of course also possible to use the magnesium salt, so that in the crystalline layer at the surface of the olefin coating calcium fluoride and magnesium fluoride are formed in crystallized form. These two salts are extremely difficult to solublize, (L CaF, 20= 3.4 X L MgF 6.4 X 10*).

Due to the reaction between the hexafluoro silicic acid salts and the alkaline calcium compounds, for example calcium hydroxide, silicic acid, Si(Ol-l) is formed which, as is known, can crystallize in chains, bands and lattices of SiO., tetrahedrons, so that an intimate crystal indentation is achieved in the coating. The chemical equation of the reaction which takes place is as follows:

MgSiF 2 (CaOI-D 2 CaF MgF Si(OI-I) The magnesium fluoride and/or calcium fluoride formed and the silicic acid form a shell or envelope with good adhesion properties on the pigment particles.

Upon application and drying of this coating, the silicic acid envelope of the pigment particles reacts with the silicic acid added in sol form, and the silicic acid particles are bonded to one another by condensation of the hydroxyl groups at the surface. The encased pigment particles are securely embedded in silicic acid film as a result.

The resultant film of pigment particles securely em bedded to the polyolefin gives to the polyolefin surface or surfaces the desired hydrophilic character and the necessary matte finish. As anti-static components for the coating, as already mentioned, a known anti-static agent, for example an alkali or ammonium salt of a polycarboxylic acid, for example polyacrylic or polymethacrylic acid or a polysulphonic acid is used. For adjusting the aqueous coatable suspension, the additives generally employed are used, and the addition of a wetting agent is necessary for the special purpose of coating the polyolefin surface.

It has been found advantageous to choose a particle diameter for the additive particles between 0.05 and 0.5 n. The optimal quantity of additive is between about 5 and 40% by weight of the dry coat.

In practical application this would mean that the composition would include as a further component a polyacryl acid propyl ester having 5% polymerized vinyl ether and a particle size of 0.05 to 0.50 pt. The quantity would be 3%, for example.

This additional component according to the invention gives the advantage that, for example, in the mass production of photographic copies in automatic developing machines the rear side of the positive images can be provided with coded impressions which contain a key for the negative, the customer and further information. Additionally, the impression adheres well and is still clearly legible after the development process. Hitherto this has been a problem which often led to great difficulties because of the high processing speed in the developing machines.

The invention will now be explained in detail with two specific embodiments, the percentages given in the examples being percents by weight and the dimension and quantity information being given in the metric system.

EXAMPLE 1 An aqueous suspension having the following composition is spread on to the surface of a photographic raw paper coated on one or both sides with polyethylene:

Remainder water The polyethylene surface of the photographic carrier material is subjected, before coating with the aqueous dispersion, to a corona irradiation for activation, in

.order to obtain a good adhesive property for the coating on the polyethylene surface. The coating itself is carried out in a manner known to the art such as an air knife, a rolling doctorknife or another known application apparatus and is then dried. The weight of the dried coating amounts to about 1 g/m. As already mentioned initially, the crystalline structure can be modified within certain limits by selecting the drying conditions, for example the temperature.

In this example there is present as a basic substance forming the foundation for this reaction, calcium magnesium carbonate in which the calcium and magnesium ions are relatively loosely bonded and react with the fluorine ions to give fluorspar and magnesium fluoride,

' whereas at the same time additional magnesium fluo- EXAMPLE 2 A photographic raw paper with a weight of about 200 g/m which is coated on both sides with a polyethylene coating by extrusion with a weight of about 35 g/m, is first given adhesive properties in accordance with Example l by corona irradiation prior to the application of an aqueous suspension of the following composition:

Specific Preferred Range Calcium hexafluoro silicate (CaSiF, ZHgO) 1.10% 0.05 6 Calcium silicate precipitate, 50-500 mu particle diameter 4.00% l l0 Silica, colloidal, 2-30 mg. particle diameter 3.00% 3 12 Acrytex (polyacrylic acid by Rohm) as a potassium salt 1.50% 0.2 2.0 Triton X 100 (commercial product) 0.05% 0.01 0.15 Butanol 4.00% 2 6 Methanol 2.00% 2 15 Remainder Water Triton X 100 is preferably used as a 5% aqueous solution and is a wetting agent which is marketed under this name by the firm of Rohm & Haas. Butanol and methanol are present in the above composition as foam damping agents.

To produce a coated photographic carrier material with a coating of polyolefin on one or both sides, the chemical compounds mentioned in Examples 1 and 2 for example are dissolved or dispersed in water in the indicated quantity and with the indicated particle size, and the dispersion obtained is applied with a known apparatus to the selected, previously activated polyolefin surface, by spreading or impression. The resultant wet strip or web of photographic carrier material provided with the applied layer is taken through a drying device in which the coating is dried, the aforesaid crystallization operation taking place during the drying time. Drying is carried out in such a manner that the carrier material is not influenced in a detrimental manner by the heat action, but the water contained in the suspension and the alcohols which may also be present such as butanol and methanol, are removed by evaporation. Drying temperatures in the region of 50 to200C are suitable for this purpose.

It has been found through the use of the aqueous suspension or solution according to the invention the disadvantages initially described can be eliminated. The admixing of an anti-static agent in the solution makes it possible to obviate electrostatic charges and the applied dry coating is easy to write upon and print upon with aqueous inks and dyestuffs. The coating gives the polymer film necessary static friction and thus obviates the self-lubricating effect of polyolefin surfaces on transport rollers and cylinders which, as mentioned initially, can cause trouble in developing machines, and it is even suitable as an adhesion-promoting coating for photographic emulsions. Owing to its mechanical strength it is also capable of standing up to mechanical stresses, for example running several times over guide and transporting rollers,,and no abrasion takes place. The coating is resistant to water and the usual chemical baths which are used for developing black and white and color photography.

As regard the coefficient of friction, the angle of slip was determined, this being increased by the effect of the applied coating according to the invention from tg a 0.4 at the non-coated polyolefin surface to tg a 0.6.

The antistatic properties when using the coating according to the invention with incorporated anti-static agent showed a reduction in the surface resistance of the polyolefin coating from 10 to 10 Ohm/cm of non-treated surface to 10 7 to 10 8 Ohm/cm of the surface treated according to the invention (measurement in accordance with German Standard DIN 53 482). These are excellent values which guarantee troublefree processing of such material.

The measuring of the coefficient of friction of the polyolefin coating is carried out in a manner known per se on an oblique plane as is usual in this art.

In Examples 1 and 2 calcium magnesium carbonate precipitate and calcium silicate precipitate are used. These compounds form a matting agent which gives a matte appearance to the polyolefin surfaces coated with the agent according to the invention. But this matting agent may also consist of precipitated calcium carbonate or mixtures of the two precipitation products, namely calcium silicate or calcium carbonate. It is also possible to replace some of the calcium by aluminum or magnesium, and the particle size should preferably be between 0.1 and 20 t. It is important that the matting agent include a fraction in which the calcium or magnesium is present as oxide, hydroxide or in the form of another alkaline-reacting calcium or magnesium compound. As is known to the art, it is, for example, also possible to produce these matting agents in their various mixtures by precipitating them by double reaction in the suspension, for example between a water soluble salt of calcium, possibly with addition of magnesium and aluminum salts on the one hand and sodium or potassium silicates or carbonates on the other hand.

In a similar manner instead of the salts of hexafluoro silicic acids mentioned in the Examples, it is also possible to use zinc and lead salts or mixtures of such salts.

It is important at any rate that the salts concerned are readily soluble salts of hexafluoro silicic acid, i.e., they are readily soluble in water.

In addition to the use of polyacryl acid propyl ester and an anti-static agent, a polyacryl butyl ester or a styrene butadiene interpolymer having a butadiene content of over 50% can be used.

Similarly, the matting agent can be calcium carbonate or the precipitated double reaction product of a water soluble salt of calcium and a magnesium and/or aluminum salt with sodium or potassium silicate or carbonate.

What we claim is:

l. A polyolefin coated photographic carrier paper receptive to hydrophilic substances, wherein said polyolefin is coated with a crystallized coating comprising calcium, magnesium, zinc or lead fluoride or mixtures thereof, silicic acid and a matting agent.

2. A photographic carrier according to claim 1 which includes in said crystallized coating an anti-static agent.

3. A photographic carrier according to claim 2 wherein said anti-static agent is an alkali or ammonium salt of a polycarboxylic or polysulphonic acid.

4. A photographic carrier according to claim 1 wherein said polyolefin is corona discharge activated.

5. A process for treating a hydrophobic, polyolefin coated photographic carrier paper to render the polyolefin coating receptive to hydrophilic substances which comprises coating said carrier with an aqueous suspension comprising:

0.05 to 6 weight magnesium or calcium hexafluoro silicate, or mixtures thereof;

1 to 10 weight matting agent;

3 to 12 weight colloidal silica;

the balance being water; and drying said coating to produce a crystallized coating bonded to the polyolefin coating.

6. A process according to claim 5 wherein said suspension includes, as a matting agent, calcium magnesium carbonate having a 2-20 p. particle size.

7. A process according to claim 5 wherein said colloidal silica has a 2-30 m p. particle size.

8. A process according to claim 5 which includes an anti-static agent.

9. A process according to claim 8 wherein said antistatic agent comprises the sodium salt of polystyrene sulphonic acid.

10. A process according to claim 8 wherein said antistatic agent is a potassium salt of polyacrylic acid.

1 l. A process according to claim 5 wherein said suspension includes, as a matting agent, calcium silicate having a 50-500 m p. particle size.

12. A process according to claim 5 wherein said suspension includes butanol or methanol.

13. A process according to claim 5 wherein said suspension includes, as a matting agent, a mixed precipitation product of calcium silicate and calcium magnesium carbonate with a particle size of about 0.1 and 20 14. A process according to claim 13 wherein a portion of the calcium is replaced by aluminum or magnesium.

15. A process according to claim 14 wherein a portion of the calcium is present in the form of an oxide, hydroxide or other alkaline reacting compound.

16. A process according to claim 5 wherein the suspension contains 5-40% of a finely dispersed polyacrylic propyl ester having a particle size of 0.05 0.50 11..

17. A process according to claim 16 wherein said ester contains 5% polymerized vinyl ether.

18. A process according to claim 5 wherein the suspension includes a polyacryl acid propyl ester, a polyacryl butyl ester or a styrene butadiene interpolymer having a butadiene content of over 50%.

19. A process according to claim 5 wherein said matting agent is calcium carbonate or the precipitated double reaction product of a water soluble salt of calcium and a magnesium and/or aluminum salt with sodium or potassium silicate or carbonate.

20. A process according to claim 5 wherein said suspension includes 0.01 to 0.2% by weight wetting agent.

* III 

1. A POLYOLEFIN COATED PHOTOGRAPHIC CARRIER PAPER RECEPTIVE TO HYDROPHILIC SUBSTANCES, WHEREIN SAID POLYOLEFIN IS COATED WITH A CRYSTALLIZED COATING COMPRISING CALCUIM, MAGNESIUM, ZINC OR LEAD FLUORIDE OR MIXTURES THEREOF, SILICIC ACID AND A MATTING AGENT.
 2. A photographic carrier according to claim 1 which includes in said crystallized coating an anti-static agent.
 3. A photographic carrier according to claim 2 wherein said anti-static agent is an alkali or ammonium salt of a polycarboxylic or polysulphonic acid.
 4. A photographic carrier according to claim 1 wherein said polyolefin is corona discharge activated.
 5. A process for treating a hydrophobic, polyolefin coated photographic carrier paper to render the polyolefin coating receptive to hydrophilic substances which comprises coating said carrier with an aqueous suspension comprising: 0.05 to 6 weight % magnesium or calcium hexafluoro silicate, or mixtures thereof; 1 to 10 weight % matting agent; 3 to 12 weight % colloidal silica; the balance being water; and drying said coating to produce a crystallized coating bonded to the polyolefin coating.
 6. A process according to claim 5 wherein said suspension includes, as a matting agent, calcium magnesium carbonate having a 2-20 Mu particle size.
 7. A process according to claim 5 wherein said colloidal silica has a 2-30 m Mu particle size.
 8. A process according to claim 5 which includes an anti-static agent.
 9. A process according to claim 8 wherein said anti-static agent comprises the sodium salt of polystyrene sulphonic acid.
 10. A process according to claim 8 wherein said anti-static agent is a potassium salt of polyacrylic acid.
 11. A process according to claim 5 wherein said suspension includes, as a matting agent, calcium silicate having a 50-500 m Mu particle size.
 12. A process according to claim 5 wherein said suspension includes butanol or methanol.
 13. A process according to claim 5 wherein said suspension includes, as a matting agent, a mixed precipitation product of calcium silicate and calcium magnesium carbonate with a parTicle size of about 0.1 and 20 Mu .
 14. A process according to claim 13 wherein a portion of the calcium is replaced by aluminum or magnesium.
 15. A process according to claim 14 wherein a portion of the calcium is present in the form of an oxide, hydroxide or other alkaline reacting compound.
 16. A process according to claim 5 wherein the suspension contains 5-40% of a finely dispersed polyacrylic propyl ester having a particle size of 0.05 - 0.50 Mu .
 17. A process according to claim 16 wherein said ester contains 5% polymerized vinyl ether.
 18. A process according to claim 5 wherein the suspension includes a polyacryl acid propyl ester, a polyacryl butyl ester or a styrene butadiene interpolymer having a butadiene content of over 50%.
 19. A process according to claim 5 wherein said matting agent is calcium carbonate or the precipitated double reaction product of a water soluble salt of calcium and a magnesium and/or aluminum salt with sodium or potassium silicate or carbonate.
 20. A process according to claim 5 wherein said suspension includes 0.01 to 0.2% by weight wetting agent. 